1. Field of the Invention
The present invention relates in general to a belt-type power transmitting system which transmits power by using an endless belt, and more particularly to a belt-type power transmitting system which transmits the power of an automotive internal combustion engine to a power consuming auxiliary device of the engine.
2. Description of the Prior Art
In general, power consuming auxiliary devices, such as an alternator, a compressor of an air conditioner, a pump of a power steering device, or the like, are driven by an output shaft of the engine through a belt-type power transmitting system. In order to effectively transmit the power of the engine to such auxiliary devices, it is important to minimize the slippage of the belt relative to the associated driving and driven pulleys about which the belt passes. Hitherto, for achieving minimization of the belt slippage, an idler pulley is employed which is arranged to contact the belt to provide the same with a constant predetermined amount of tension. Usually, in order to assure the transmission of power from the engine to the auxiliary device even when the auxiliary device is providing a heavy load, the idler pulley is set to be constantly strongly pressed against the belt to provide the high tension needed for heavy loads. However, this means that high tension is constantly applied to the belt, even when the auxiliary device is producing a relatively light load condition requiring only a light belt tension for minimizing the belt slippage. Accordingly, this arrangement is inadvisable since this constant high tension shortens the life of the belt.